1. Field of the Invention
The present invention relates to a connecting structure for an exhaust pipe.
2. Description of the Related Art
An exhaust passage for guiding exhaust gas from an engine sometimes includes a plurality of separate exhaust pipes connected together. In the case of an outboard motor, for example, restrictions on the shape and layout of an exhaust pipe are severe because space is limited inside a housing enclosing the engine. Consequently, it is difficult to make the exhaust pipe have a linear shape and the shape is often complex. In such a case, since it is difficult to form the exhaust pipe as a one-piece integral unit, an exhaust passage is made by connecting a plurality of exhaust pipes together. When a plurality of exhaust pipes are connected together in this way, O-rings and other seal members must be provided at the connecting portions of the exhaust pipes as is demonstrated in, for example, Japanese Laid-open Patent Application No. 2010-248909.
However, the seal members are generally made of a resin material. Consequently, the seal members are susceptible to damage caused by heat from exhaust gas. Therefore, it is necessary to provide a structure to protect the seal members from the heat of the exhaust gas. In Japanese Laid-open Patent Application No. 2003-74351, for example, a seal member is arranged between a first exhaust passage and a second exhaust passage and a structure is disclosed in which an external wall of the first exhaust passage and an internal surface of the second exhaust passage are in close contact with each other.
However, with the structure disclosed in Japanese Laid-open Patent Application No. 2003-74351, a gap develops between the first exhaust passage and the second exhaust passage due to a difference in amounts of thermal expansion undergone by the first exhaust passage and the second exhaust passage. When such a gap occurs between the first exhaust passage and the second exhaust passage, exhaust gas enters through the gap and the seal member is exposed to the exhaust gas. As a result, the seal member is damaged by heat of the exhaust gas. Thus, with the structure disclosed in Japanese Laid-open Patent Application No. 2003-74351, it is difficult to prevent the seal member from being exposed to exhaust gas.